1. Field of the invention
The present invention relates generally to machine tools, and in particular to an apparatus and related method for establishing alignment between a machine tool's spindle and its work table.
2. Description of the Prior Art
During the operation of a machine tool such as a drill press, or milling device having a spindle depending vertically over a work surface or table, it is necessary to establish either perpendicularity or another known angular relationship between the spindle and table. A work piece situated on the work surface of the machine tool may have to have several machining operations performed on it as the work progresses. During each machining operation, the alignment between the machine tool spindle and the work surface of the machine is critical. The constant readjustment and realignment of the machine tool spindle relative to the machine tool work surface can be a time consuming task, with accuracy based on the manual skill of the machine operator.
The most primitive efforts to attain proper alignment have involved the use of levels placed upon the work surface of the machine tool, and then using the table adjustment to level the work surface. The disadvantage of these devices is that although the surface may be level, there are no assurances that the machine tool spindle is properly aligned with the surface. Many modern machine tools have spindle arms which are adjustable through large angles, as discussed in U.S. Pat. No. 4,437,803 to Volna.
Consequently, the industry has developed various "feeler gauge" type devices for squaring the spindle directly to the work surface. Such devices require direct physical contact of the feeler with the work surface to determine the proximity of the spindle to the work surface, and have indicator gauges to show the proximity as relative distance. By equalizing the proximity at various points to make the gauge or gauges read the same, as by adjusting either the spindle or the table, a direct orthogonal plane can be established with such devices. The "feeler" proximity indicators may be rollers such as described in the above referenced patent, or resiliently urged fingers such as disclosed in U.S. Pat. No. 4,406,069 to Clement.
However, such devices require time consuming calibration. For example, the 4,406,069 patent requires at least three spring-urged fingers, and is calibrated for each use by locating a gauge block on the work surface and rotating each finger over it, then adjusting both course and fine adjustment knobs to give each gauge a common "zero setting". The block is then removed and the table or spindle arm adjusted to make each gauge read the same.
Further, such devices are predicated upon a smooth work surface. Most machine tools are manufactured with T-slots or parallel grooves on the work surface to clamp a work piece to the work surface while it is being machined. Other holes or indents may eventually be caused on the work surface by general wear and tear and accidental machining operations. It is also common to have debris, left over from previous machining operations, deposited on top of the work surface. Since the devices in the prior art all rely on physical contact with the work surface, a marred or dirty work surface may produce an inaccurate alignment.
Finally, an inadvertently large adjustment or an adjustment in the wrong direction while the alignment device is in contact with the work surface may damage these devices.